1,495 research outputs found
An exceptional X-ray view of the young open cluster NGC 6231: what XMM-Newton has taught us
Considered as the core of the Sco OB1 association, the young open cluster NGC
6231 harbours a rich O-type star population. In 2001, the XMM-Newton satellite
targeted the cluster for a nominal duration of about 180 ks. Thanks to the
detector sensitivity, the EPIC cameras provided an unprecedented X-ray view of
NGC 6231, revealing about 600 point-like sources. In this contribution, we
review the main results that have been obtained thanks to this unprecedented
data set. Concerning the O-type stars, we present the latest developments
related to the so-called 'canonical' Lx-Lbol relation. The dispersion around
this relation might actually be much smaller than previously thought. In our
data set, the sole mechanism that yields a significant deviation from this
scheme is wind interaction. It is also the sole mechanism that induces a
significant variation of the early-type star X-ray flux. In a second part of
this contribution, we probe the properties of the optically faint X-ray
sources. Most of them are believed to be low mass pre-main sequence stars.
Their analysis provides direct insight into the star formation history of the
cluster.Comment: 6 pages, 5 figures, to appear in "The X-Ray Universe 2005", ESA
Symposium held at El Escorial, Madrid (Spain), 26-30 Sep 200
The massive star binary fraction in young open clusters I. NGC 6231 revisited
We present the results of a long-term high-resolution spectroscopy campaign
on the O-type stars in NGC 6231. We revise the spectral classification and
multiplicity of these objects and we constrain the fundamental properties of
the O-star population. Almost three quarters of the O-type stars in the cluster
are members of a binary system. The minimum binary fraction is 0.63, with half
the O-type binaries having an orbital period of the order of a few days. The
eccentricities of all the short-period binaries are revised downward, and
henceforth match a normal period-eccentricity distribution. The mass-ratio
distribution shows a large preference for O+OB binaries, ruling out the
possibility that, in NGC 6231, the companion of an O-type star is randomly
drawn from a standard IMF. Obtained from a complete and homogeneous population
of O-type stars, our conclusions provide interesting observational constraints
to be confronted with the formation and early-evolution theories of O stars.Comment: 16 pages, 14 figures. Accepted by MNRA
The Struve-Sahade effect in the optical spectra of O-type binaries I. Main-sequence systems
We present a spectroscopic analysis of four massive binary systems that are
known or are good candidates to display the Struve-Sahade effect (defined as
the apparent strengthening of the secondary spectrum of the binary when the
star is approaching, and the corresponding weakening of the lines when it is
receding).
We use high resolution optical spectra to determine new orbital solutions and
spectral types of HD 165052, HD 100213, HD 159176 and DH Cep. As good knowledge
of the fundamental parameters of the considered systems is necessary to examine
the Struve-Sahade effect. We then study equivalent width variations in the
lines of both components of these binaries during their orbital cycle.
In the case of these four systems, variations appear in the equivalent widths
of some lines during the orbital cycle, but the definition given above can any
longer be valid, since it is now clear that the effect modifies the primary
spectrum as much as the secondary spectrum. Furthermore, the lines affected,
and the way in which they are affected, depend on the considered system. For at
least two of them (HD 100213 and HD 159176) these variations probably reflect
the ellipsoidal variable nature of the system.Comment: 12 pages, 20 figures, in press A&
The atypical emission-line star Hen3-209
We analyse observations, spanning 15 years, dedicated to the extreme
emission-line object Hen3-209. Our photometric data indicate that the
luminosity of the star undergoes marked variations with a peak-to-peak
amplitude of 0.65mag. These variations are recurrent, with a period of
16.093+-0.005d. The spectrum of Hen3-209 is peculiar with many different lines
(HI, HeI, FeII,...) showing P Cygni profiles. The line profiles are apparently
changing in harmony with the photometry. The spectrum also contains [OIII]
lines that display a saddle profile topped by three peaks, with a maximum
separation of about 600km/s. Hen3-209 is most likely an evolved luminous object
suffering from mass ejection events and maybe belonging to a binary system.Comment: 6p, 5 fig, accepted for publication in MNRAS
(www.blackwell-synergy.com
Observational signatures of past mass-exchange episodes in massive binaries: The case of LSS 3074
The role of mass and momentum exchanges in close massive binaries is very
important in the subsequent evolution of the components. Such exchanges produce
several observational signatures such as asynchronous rotation and altered
chemical compositions, that remain after the stars detach again. We
investigated these effects for the close O-star binary LSS 3074 (O4 f + O6-7
:(f):), which is a good candidate for a past Roche lobe overflow (RLOF) episode
because of its very short orbital period, P = 2.185 days, and the luminosity
classes of both components. We determined a new orbital solution for the
system. We studied the photometric light curves to determine the inclination of
the orbit and Roche lobe filling factors of both stars. Using phase-resolved
spectroscopy, we performed the disentangling of the optical spectra of the two
stars. We then analysed the reconstructed primary and secondary spectra with
the CMFGEN model atmosphere code to determine stellar parameters, such as the
effective temperatures and surface gravities, and to constrain the chemical
composition of the components. We confirm the apparent low stellar masses and
radii reported in previous studies. We also find a strong overabundance in
nitrogen and a strong carbon and oxygen depletion in both primary and secondary
atmospheres, together with a strong enrichment in helium of the primary star.
We propose several possible evolutionary pathways through a RLOF process to
explain the current parameters of the system. We confirm that the system is
apparently in overcontact configuration and has lost a significant portion of
its mass to its surroundings. We suggest that some of the discrepancies between
the spectroscopic and photometric properties of LSS 3074 could stem from the
impact of a strong radiation pressure of the primary
The first orbital solution for the massive colliding-wind binary HD93162 (=WR25)
Since the discovery, with the EINSTEIN satellite, of strong X-ray emission
associated with HD93162 (=WR25), this object has been predicted to be a
colliding-wind binary system. However, radial-velocity variations that would
prove the suspected binary nature have yet to be found. We spectroscopically
monitored this object to investigate its possible variability to address this
discordance. We compiled the largest available radial-velocity data set for
this star to look for variations that might be due to binary motion. We derived
radial velocities from spectroscopic data acquired mainly between 1994 and
2006, and searched these radial velocities for periodicities using different
numerical methods. For the first time, periodic radial-velocity variations are
detected. Our analysis definitively shows that the Wolf-Rayet star WR25 is an
eccentric binary system with a probable period of about 208 days.Comment: 7 pages, 4 figures, accepted by A+
Evidence for a physically bound third component in HD 150136
Context. HD150136 is one of the nearest systems harbouring an O3 star.
Although this system was for a long time considered as binary, more recent
investigations have suggested the possible existence of a third component.
Aims. We present a detailed analysis of HD 150136 to confirm the triple nature
of this system. In addition, we investigate the physical properties of the
individual components of this system. Methods. We analysed high-resolution,
high signal-to-noise data collected through multi-epoch runs spread over ten
years. We applied a disentangling program to refine the radial velocities and
to obtain the individual spectra of each star. With the radial velocities, we
computed the orbital solution of the inner system, and we describe the main
properties of the orbit of the outer star such as the preliminary mass ratio,
the eccentricity, and the orbital-period range. With the individual spectra, we
determined the stellar parameters of each star by means of the CMFGEN
atmosphere code. Results. We offer clear evidence that HD 150136 is a triple
system composed of an O3V((f\ast))-3.5V((f+)), an O5.5-6V((f)), and an
O6.5-7V((f)) star. The three stars are between 0-3 Myr old. We derive dynamical
masses of about 64, 40, and 35 Msun for the primary, the secondary and the
third components by assuming an inclination of 49{\deg}. It currently
corresponds to one of the most massive systems in our galaxy. The third star
moves with a period in the range of 2950 to 5500 d on an outer orbit with an
eccentricity of at least 0.3. This discovery makes HD 150136 the first
confirmed triple system with an O3 primary star. However, because of the long
orbital period, our dataset is not sufficient to constrain the orbital solution
of the tertiary component with high accuracy.Comment: 13 pages, 11 figures, accepted at A&
A new investigation of the binary HD 48099
With an orbital period of about 3.078 days, the double-lined spectroscopic
binary HD 48099 is, still now, the only short-period O+O system known in the
Mon OB2 association. Even though an orbital solution has already been derived
for this system, few information are available about the individual stars. We
present, in this paper, the results of a long-term spectroscopic campaign. We
derive a new orbital solution and apply a disentangling method to recover the
mean spectrum of each star. To improve our knowledge concerning both
components, we determine their spectral classifications and their projected
rotational velocities. We also constrain the main stellar parameters of both
stars by using the CMFGEN atmosphere code and provide the wind properties for
the primary star through the study of IUE spectra. This investigation reveals
that HD 48099 is an O5.5 V((f))+O9 V binary with M_1 sin^3 i = 0.70 M_{\sun}
and M_2 sin^3 i = 0.39 M_{\sun}, implying a rather low orbital inclination.
This result, combined with both a large effective temperature and log g,
suggests that the primary star (v sini ~ 91 km s^-1) is actually a fast rotator
with a strongly clumped wind and a nitrogen abundance of about 8 times the
solar value.Comment: 12 pages, 7 figures, accepted by Ap
Constraining the fundamental parameters of the O-type binary CPD-41degr7733
Using a set of high-resolution spectra, we studied the physical and orbital
properties of the O-type binary CPD-41 7733, located in the core of \ngc. We
report the unambiguous detection of the secondary spectral signature and we
derive the first SB2 orbital solution of the system. The period is 5.6815 +/-
0.0015 d and the orbit has no significant eccentricity. CPD-41 7733 probably
consists of stars of spectral types O8.5 and B3. As for other objects in the
cluster, we observe discrepant luminosity classifications while using
spectroscopic or brightness criteria. Still, the present analysis suggests that
both components display physical parameters close to those of typical O8.5 and
B3 dwarfs. We also analyze the X-ray light curves and spectra obtained during
six 30 ks XMM-Newton pointings spread over the 5.7 d period. We find no
significant variability between the different pointings, nor within the
individual observations. The CPD-41 7733 X-ray spectrum is well reproduced by a
three-temperature thermal mekal model with temperatures of 0.3, 0.8 and 2.4
keV. No X-ray overluminosity, resulting e.g. from a possible wind interaction,
is observed. The emission of CPD-41 7733 is thus very representative of typical
O-type star X-ray emission.Comment: Accepted by ApJ, 15 pages, 9 figure
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